1. Field of the Invention
This invention relates to semiconductor light-emitting devices such as semiconductor lasers, light-emitting diodes, etc. and in particular relates to semiconductor light-emitting devices having emission wavelengths in a range which includes the blue to ultra-violet region of the spectrum.
2. Description of the Prior Art
In recent years semiconductor lasers have been realized in practice, which utilize AlGaAs/GaAs III-V semiconductor materials. When a semiconductor laser is used in a data processing application such as data readout from an optical disc, or in a laser printer, it is desirable that the emission wavelength of the light produced from the semiconductor laser should be as short as possible, in order to maximize the data processing performance. However with semiconductor lasers that have been utilized hitherto, even if the activation layer of the laser is formed of a material such as AlGaInP, which has a large size of forbidden energy gap and is among the direct-transition type III-V semiconductor materials, it is only possible to achieve an emission wavelength that is in the range 580 to 690 nm. Thus, the emission wavelength cannot be made sufficiently short to reach the blue region of the visible spectrum. Another direct-transition type compound semiconductor material which has an even larger value of forbidden energy gap is Zn(SSe), which is a II-VI compound semiconductor. There is a possibility to achieve a semiconductor laser having a shorter wavelength of the emission light with the double-heterostructure. However, due to the difficulty encountered in controlling p-type conduction in this material, it has not been possible to utilize it practically to obtain emission in the blue to ultra-violet region of the spectrum up to the present.
On the other hand, the possibility of production of pn junction type light-emitting devices is known which is obtained by combining n-type II-VI compound semiconductor and p-type chalcopyrite type compound semiconductor. Sigurd Wagner; Journal of Applied Physics, Vol. 45, No. 1, January (1974) p246 and Satoshi Kobayashi et al.; Japanese Journal of Applied Physics, Vol. 30 NO. 10A, October (1991), pp. L1747, describe methods of production of hetero-junction diodes by combining II-VI compound semiconductor and chalcopyrite type compound semiconductor which are materials having a large size of forbidden energy gap. The former reported that a green light emission was obtained with combination of CdS-CuGaS.sub.2. The latter reports a green light emission with combination of ZnS-CuGaS.sub.2.
As mentioned above, there is a need for a capability for practical manufacture of semiconductor light-emission devices having wavelengths in a range which includes the blue to ultra-violet region of the spectrum. The inventor studied a lot of combinations of II-VI compound semiconductor and chalcopyrite type compound semiconductor. As result, the inventor found a new combination of II-VI compound semiconductors and chalcopyrite type compound semiconductors for providing wavelengths in a range which includes the blue to ultra-violet region of the spectrum.